This application is a U.S. national state application of copending International Application Ser. No. PCT/JP99/04892, filed Sep. 8, 1999, and claiming a priority date of Sep. 17, 1998, and published in a non-English language.
1. Field of the Invention
The present invention relates to a medium for recording information reproducible by utilizing near-field light and an information reproducing apparatus and an information recording and reproducing apparatus for reproducing information recorded in the information recording medium at a high density, particularly to an information recording medium and an information reproducing apparatus capable of providing a reproduced signal having a large intensity and an information recording and reproducing apparatus having high reliability and capable of carrying out high-speed recording.
2. Background Information
A number of present information reproducing apparatus carry out information reproduction on a magnetic disk or an optical disk as an information recording medium. In particular, a CD, which is one of optical disks enabling information recording at a high density and mass production at low cost, is widely utilized as a medium for recording information having a large capacity. The CD is formed with pits having a size of a wavelength of laser beam used in reproduction and a depth of about a quarter of the wavelength on its surface to thereby enable a reading operation utilizing an interference phenomenon of light.
In reading recorded information from an optical disk represented by CD, generally, there is utilized a lens optical system used in an optical microscope. Hence, when information recording density is increased by reducing the size or the track pitch of a pit, due to a problem of a diffraction limit of light, the system runs into a wall that a spot size of laser beam cannot be made a half wavelength or smaller and an information recording unit cannot be constituted by a size smaller than the wavelength of laser beam.
Further, not only in an optical disk but also in a magneto-optical disk recording information by a magneto-optical recording system and a phase change recording system, recording and reproduction of information at a high density is realized by a very small spot of laser beam and therefore, the information recording density is restricted by the diameter of the spot provided by focusing laser beam.
Hence, in order to break though the restriction by the diffraction limit, there has been proposed an information reproducing apparatus using an optical head provided with a very small aperture having a diameter equal to or smaller than the wavelength of laser beam utilized for reproduction, for example, about 1/10 of the wavelength and utilizing near-field light (including both of near-field light and far-field light) generated at the very small aperture portion.
Inherently, there is provided a near-field microscope using a probe having the above-described very small aperture as an apparatus of utilizing near-field light and the near-field microscope is utilized for observation of a very small surface structure of a sample. As one of near-field light utilizing systems in a near-field microscope, there is provided a system (illumination mode) in which a distance between a very small aperture of a probe and a surface of a sample is reduced to a degree of a diameter of the very small aperture of the probe and propagated light is introduced via the probe and toward the very small aperture of the probe, thereby, near-field light is generated at the very small aperture. In this case, scattered light produced by an interaction between the generated near-field light and the surface of the sample, is detected by a scattered light detecting system by being accompanied by intensity or phase reflected with a fine structure of the surf ace of the sample and there is enabled observation having a high resolution which cannot be realized by a conventional optical microscope.
Further, as another system of a near-field microscope utilizing near-field light, there is provided a system in which near-field light is localized at the surface of a sample by irradiating propagated light toward a sample and a very small aperture of a probe is made proximate to the surface of the sample up to a degree of the diameter of the very small aperture of the probe (collection mode). In this case, scattered light produced by interaction between the localized near-field light and the very small aperture of the probe, is introduced to a scattered light detecting system via the very small aperture of the probe by being accompanied by the intensity or phase reflected with a fine structure of the surface of the sample to thereby achieve observation having a high resolution.
Information reproducing apparatus utilizing the above-described near-field light, utilizes these observation systems in the near-field microscope and by utilizing the near-field light, information reproduction of an information recording medium recorded with information at a higher density can be carried out.
In such an information reproducing apparatus, as a probe for reproducing information, there is particularly proposed use of a planer probe without a sharpened front end. FIG. 14 is a view showing a conventional planer probe utilizing near-field light and an information recording medium. In FIG. 14, a planer probe 101 is formed with an aperture having an inverse pyramid structure on a planer substrate and particularly, an apex portion of the aperture is penetrated by a very small aperture 102 having a diameter of several tens nanometers. According to the planer probe 101, near-field light 107 is generated at a vicinity of the very small aperture 102 by irradiating laser beam 106 toward the very small aperture 102.
The near-field light 107 is scattered by a data mark 105 particularly showing strong interaction between the near-field light and the data mark and produces propagated light 108 at an information recording medium 104. The propagated light 108 is introduced to a light receiving element 103 provided at a vicinity of the very small aperture 102 of the planer probe 101 and is detected as a reproduced signal.
As described above, the planer probe is constructed by a constitution in which both of the very small aperture 102 for generating the near-field light 107 and the light receiving element 103 for detecting the propagated light 108 scattered from the data mark 105, are arranged on a side of a surface of the information recording medium 104 (reflection mode) and therefore, downsizing of an information reproducing apparatus can be achieved, further, the planer probe can be formed by using the semiconductor fabrication technology and accordingly, mass production having high reproducibility is realized and the planer probe is pertinently used as an optical head of the information reproducing apparatus utilizing the near-field light.
Further, high density information recording can be carried out also by changing a state, for example, a crystal state of the surface of the information recording medium by interaction between the near-field light generated from the probe and the information recording medium.
However, in using the planer probe 101, in order to provide the propagated light 108 scattered from the data mark 105, since the propagated light 108 is defined as light having a wavelength of several 100 nm, it is necessary to make a distance xe2x80x9caxe2x80x9d from the data mark 105 or the very small aperture 106 to the light receiving element 103 equal to or larger than the wavelength. In this case, a clearance xe2x80x9cdxe2x80x9d between the very small aperture 102 and the information recording medium 104 is generally provided with a value equal to or smaller than 100 nm in order to achieve sufficiently large interaction between the near-field light 107 generated at the very small aperture 102 and the data mark 105 on the information recording medium 104. Therefore, in the clearance xe2x80x9cdxe2x80x9d, the propagated light 108 is detected only at a location separated from the data mark 105 by at least several 100 nm or more in a direction in parallel with the surface of the information recording medium 104.
Generally, since the near-field light 107 is introduced from right above the data mark 105, an essential intensity distribution of the propagated light 108 produced by being scattered by the data mark 105, indicates a small value with respect to a component of the propagated light in the direction in parallel with the surface of the information recording medium 104. Further, since the clearance xe2x80x9cdxe2x80x9d is provided with a sufficiently small value, a light amount of the propagated light 108 cannot be provided sufficiently.
Further, as an information reproducing apparatus, there can be selected a constitution in which the substrate of the information recording medium 104 is formed by a light transmitting member and the propagated light 108 scattered from the data mark 105 is detected at a rear face of the information recording medium 104 (transmission mode), however, it is necessary to install a light receiving element on the rear face side of the information recording medium 104, which results in large-sized formation of the apparatus.
Further, recording can be carried out also by generating near-field light by using the above-described planer type near-field optical head and by changing, for example, a crystal state of a surface of an information recording medium as an information recording apparatus. In this case, it is necessary to provide some assisting energy to the surface of the information recording medium since the intensity of the near-field light is very low. This is referred to as assist light. The assist light is irradiated to the data mark by propagating the assist light in a direction right reverse to that of the propagated light 108 in FIG. 14, which provides energy at a level which is slightly smaller than the threshold of energy necessary for changing the state of the surface of the information recording medium. By adding energy of the near-field light irradiated from the near-filed optical head to the energy of the assist light, there is provided the energy exceeding the above-described threshold and the state of the surface of the information recording medium is changed, which constitutes recording of information.
In order to carry out information recording by such a method, it is necessary to irradiate assist light to the data mark stably with sufficient intensity, however, similar to the propagated light in the information reproducing apparatus, there poses a problem that a space for propagating the assist light is insufficient. That is, it is necessary to make the near-field optical head and the surface of the information recording medium proximate to each other such that the both can carry out interaction by the near-field light and it is difficult that the assist light which is propagated light invades the small clearance. Therefore, the assist light having sufficient intensity cannot reach the data mark and the data mark cannot be provided with energy necessary for recording even by adding the near-field light from the near-field optical head.
In view of the above-described problems, it is an object of the invention to provide an information recording medium capable of providing a reproduced signal having a sufficiently large intensity of information recorded at a high density, an information reproducing apparatus achieving downsized formation by the information recording medium and an information recording and reproducing apparatus having high speed and high reliability.
In order to achieve the above-described object, a first information recording medium according to the invention is characterized in that in an information recording medium formed with information reproduced by a reproducing probe provided with a very small aperture for generating near-field light on a surface of the medium wherein the information recording medium comprises a two layer structure of a light transmitting layer for transmitting light and a light reflecting layer for reflecting light and a data mark constituting a unit of the information is formed on the light transmitting layer.
According to the invention, the first information recording medium comprises the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member and the data mark is formed above the light reflecting layer and accordingly, the propagated light generated by the interaction between the near-field light and the data mark can be reflected by the light reflecting layer via the light transmitting layer and can be emitted from the surface of the information recording medium and a sufficiently large amount of the propagated light can be provided at the surface of the information recording medium at a position remote from the data mark.
Further, a second information recording medium according to the invention in accordance with the first information recording medium according to the invention is characterized in that an interface between the light transmitting layer and the light reflecting layer is inclined in one direction.
According to the invention, the second information recording medium comprises the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member, the interface between the light transmitting layer and the light reflecting layer is inclined in one direction, the data mark is formed on the light transmitting layer and accordingly, the propagated light generated by the interaction between the near-field light and the data mark can be strongly reflected in the one direction at the light reflecting layer via the light transmitting layer and can be emitted from the surface of the light recording medium and a sufficient amount of the propagated light can be provided at the surface of the information recording medium at a position remote from the data mark on the side of the inclined face of the light reflecting layer 1.
Further, a third information recording medium according to the invention in accordance with the first information recording medium according to the invention is characterized in that a surface of the light reflecting layer constituting an interface between the light transmitting layer and the light reflecting layer, is formed in a shape of reflecting light incident on the light reflecting layer to a specific area.
According to the invention, the third information recording medium comprises the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member, the surface of light reflecting layer is formed in the shape achieving reflection of light to the specific area, the data mark 4 is formed on the light transmitting layer and accordingly, the propagated light generated by the interaction between the near-field light and the data mark, can pass the light transmitting layer, can be strongly reflected to the specific area at the light reflecting layer, can be emitted from the surface of the information recording medium and a sufficient amount of the propagated light can be provided at the specific area at a position remote from the data mark.
Further, a fourth information recording medium according to the invention in accordance with the third information recording apparatus according to the invention is characterized in that the shape constitutes a diffraction grating.
According to the invention, the fourth information recording medium comprises the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member, the diffraction grating is formed at the surface of the light reflecting layer, the data mark is formed on the light transmitting layer and accordingly, the propagated light generated by the interaction of the near-field light and the data mark can pass through the light transmitting layer, can be strongly reflected to the specific area determined by the diffraction grating at the light reflecting layer and can be emitted from the surface of the information recording medium and a sufficient amount of the propagated light can be provided at the specific area at a position remote from the data mark.
Further, a first information reproducing apparatus according to the invention is characterized in that in an information reproducing apparatus for reproducing information by a reproducing probe provided with a very small aperture for generating near-field light, the information reproducing apparatus comprising an information recording medium comprising a two layer structure of a light transmitting layer for transmitting light and a light reflecting layer for reflecting light and formed with a data mark constituting a unit of the information on the light transmitting layer, and light detecting means for detecting propagated light generated by an interaction between the near-field light and the data mark and outputting a detected signal.
According to the invention, there is used the information recording medium comprising the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member and formed with the data mark on the light reflecting layer, the propagated light provided by the information recording medium is received by the light detecting means, a reproduced signal having sufficiently large intensity indicating presence or absence of the data mark can be provided and accordingly, there can be realized downsized formation of the apparatus in the case of adopting the illumination mode and a transmission mode constituting a system of information reproduction utilizing near-field light and there can be reproduced stable information having high reliability by the reproduced signal having the sufficiently large intensity.
Further, a second information reproducing apparatus according to the invention is characterized in that in an information reproducing apparatus for reproducing information by a reproducing probe provided with a very small aperture for guiding out propagated light by an interaction with near-field light, the information reproducing apparatus comprising an information recording medium comprising a two layer structure of a light transmitting layer for transmitting light and a light reflecting layer for reflecting light and formed with a data mark constituting a unit of the information on the light transmitting layer, and light irradiating means for irradiating irradiation light for generating the near-field light at the data mark to the information recording medium.
According to the invention, there is used the information recording medium comprising the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member and formed with the data mark above the light reflecting layer, the propagated light provided by the information recording medium is received by the light detecting means, a reproduced signal having a sufficiently large intensity indicating presence or absence of the data mark can be provided and accordingly, there can be realized downsized formation of the apparatus in the case of adopting the collection mode and the transmission mode constituting the system of information reproduction utilizing near-field light and there can be reproduced stable information having high reliability by the reproduced signal having the sufficiently large intensity.
Further, a third information reproducing apparatus according to the invention is characterized in that in an information reproducing apparatus for reproducing information by a reproducing probe provided with a very small aperture for generating near-field light, the information reproducing apparatus comprising an information recording medium comprising a two layer structure of a light transmitting layer for transmitting light and a light reflecting layer for reflecting light and formed with a data mark constituting a unit of the information on the light transmitting layer, first and second light detecting means for outputting detected signals by detecting propagated light generated by an interaction between the near-field light and the data mark and arranged on left and right sides of the very small aperture, difference calculating means for calculating a difference between a first detected signal outputted from the first light detecting means and a second detected signal outputted from the second light detecting means and outputting a difference signal, reproducing probe position controlling means for controlling a position of the reproducing probe in accordance with the difference signal, and reproduced signal generating means for generating a reproduced signal by calculating to add the first detected signal and the second detected signal.
According to the invention, there is used the information recording medium comprising the two layer structure of the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member and formed with the data mark above the light reflecting layer, the propagated light provided by the information recording medium can be detected in two direction relative to the very small aperture of the reproducing probe and there can be carried out tracking control of the reproducing probe by the difference between the detected two detected signals. Further, the near-field light generated at the very small aperture of the reproducing probe is utilized as a signal for tracking control and therefore, there can be carried out the tracking control having high accuracy with high positional resolution.
Further, a fourth information reproducing apparatus according to the invention in accordance with any one of the first through the third information reproducing apparatus according to the invention, is characterized in that the reproducing probe is a planer probe comprising a planer substrate formed with a hole in a shape of an inverse cone penetrated such that a top portion thereof constitutes the very small aperture and arranged with the light detecting means or the light irradiating means at the planer substrate.
According to the invention, as the reproducing probe, there is adopted the planer probe provided with the light detecting means or the light irradiating means and accordingly, further compact apparatus constitution is achieved. Further, the planer probe can be fabricated by using the semiconductor fabrication technology and accordingly, mass production having high reproducibility can be carried out.
Further, a fifth information reproducing apparatus according to the invention in accordance with the fourth information reproducing apparatus according to the invention, is characterized in that the reproducing probe carries out reproduction by a state of being inclined relative to a surface of the information recording medium.
According to the invention, the propagated light provided by the information recording medium comprising the two layer structure of the light transmitting layer and the light reflecting layer, is received by the light detecting means of the planer probe arranged to incline such that the clearance between the planer probe and the surface of the information recording medium becomes sufficiently large, there can be provided the reproduced signal having sufficiently large intensity indicating presence or absence of the data mark and accordingly, there is realized downsized formation of the apparatus in the case of adopting the transmission mode constituting one of the system of information reproduction utilizing near-field light, further, there can be reproduced stable information having high reliability by the reproduce signal having the sufficiently large intensity.
Further, a sixth information reproducing apparatus according to the invention in accordance with any one of the first through the third information reproducing apparatus according to the invention, is characterized in that the reproducing probe comprises an optical fiber a front end of which is provided with the very small aperture.
According to the invention, there can be utilized the probe of the optical fiber type used in a conventional near-field microscope as the reproducing probe and accordingly, accumulated technology of the near-field microscope is effectively applicable to the information reproducing apparatus.
Further, a seventh information reproducing apparatus according to the invention in accordance with any one of the first through the third information reproducing apparatus according to the invention, is characterized in that the reproducing probe is a probe of a cantilever type provided with the very small aperture at a projected portion thereof.
According to the invention, there can be utilized the probe of the cantilever type used in a conventional near-field microscope as the reproducing probe and accordingly, accumulated technology of the near-field microscope is effectively applicable to the information reproducing apparatus.
Further, a first information recording and reproducing apparatus according to the invention is characterized in that in an information recording and reproducing apparatus in which a recording and reproducing probe provided with a very small aperture for generating near-field light records and reproduces information to and from an information recording medium by carrying out an interaction between the recording and reproducing probe and the information recording medium via the near-field light wherein the information recording medium comprises a two layer structure of a light transmitting layer for transmitting light and a light reflecting layer for reflecting light and formed with a data mark constituting a unit of the information on the light transmitting layer, the information recording and reproducing apparatus comprising near-field light generating light irradiating means for irradiating irradiation light for generating the near-field light to the recording and reproducing probe, and propagated light irradiating means for irradiating light to the light reflecting layer such that the light is irradiated to an area at which the near-field light on the light transmitting layer carries out the interaction.
According to the invention, the first information recording and reproducing apparatus comprises the light transmitting layer comprising the light transmitting member and the light reflecting layer comprising the light reflecting member and formed with the data mark above the light reflecting layer and accordingly, the data mark can be irradiated not only by the near-field light from the probe but by the light from the light reflecting layer and larger energy can be provided by the data mark.
Further, according to a second information recording and reproducing apparatus according to the invention in accordance with the first information recording and reproducing apparatus according to the invention, is characterized in that the light irradiated to the light reflecting layer is provided with an intensity and a wavelength for assisting the near-field light for recording the information.
According to the invention, energy necessary for information recording can be provided not only by the near-field light from the probe but also from assist light from the light reflecting layer and by changing a state of the surface of the information recording medium by controlling very weak near-field light, recording having high reliability can be carried out at high speed.